"It has been the most effective tool we have in dealing with blackbirds," he said.

Last year in North Dakota, about 3,700 acres of wetlands in seven counties were treated, Mastrangelo said.

A herbicide is applied in late summer from a helicopter, at a cost to the government of about $22 an acre, Mastrangelo said. The agency had hoped to treat double the amount of wetlands last year but the cost of the herbicide doubled, he said.

"The increased cost in herbicide reduced the amount of acres we could treat," Mastrangelo said.

The amount of acres that will be treated this year is still unknown, he said.

"We won't know for at least a couple of months if the herbicide stabilizes in price, goes up or hopefully goes down," he said.

The program targets only cattails on private land and is free to sunflower farmers.

Kleingartner said blackbirds eat more than $20 million worth of sunflowers each year in North Dakota, which accounts for about half the nation's sunflower production.

Some 70 million blackbirds come through the Northern Plains each year, including about 6 million that stop in North Dakota, biologists say. Each blackbird can eat about an ounce of sunflower seeds daily.

Cattails cover some 600,000 acres of wetlands in North Dakota. Mastrangelo said wetlands treated with the herbicide are typically free of cattails for about five years.

Noise cannons also are used to shoo blackbirds off sunflower fields.

Sometimes nothing works, so farmers have either quit growing the crop or planted in other areas, Kleingartner said.

"Some farmers have just found out that they can't competitively produce the crop without blackbird damage," he said.

Increased corn production in North Dakota has helped sunflower farmers some, Kleingartner said.

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